1. Field of the Invention
The present invention relates in general to a spectrophotometer and in particular to a multifunctional spectrophotometer which allows a plurality of various measurements.
2. Description of the Prior Art
A spectrophotometer has been hitherto known which utilizes generally a plane grating as a dispersing element, a concave mirror as an element for collimating or converging a light beam, and a photomultiplier as a detector. It is also known that a monochromator composed of a concave grating which makes unnecessary the use of the concave mirror mentioned above can be employed for the purposes of reducing stray light and improving the aberration. However, since the concave grating requires high skill in manufacture thereof and thus becomes expensive, and is further attended by the undesirable astigmatism inherent thereto, the concave grating has not been widely employed but has been found its application only in extremely ultra violet spectrophotometers. Lately, a holographic grating has become available which is manufactured by utilizing a laser holography technic. However, such holographic grating has drawbacks that the wavelength of the diffracted light from the grating as well as the position at which the image is formed are subjected to some restriction imposed by a specific wavelength of the laser used in the manufacture of the grating. Further, because the grooves of the grating is formed by processing interference fringes photographically, the cross-section of the grooves can not be freely selected as in the case of the mechanically ruled grating lines, which makes it difficult to attain a high diffraction efficiency at a given wavelength region.